Polybenzimidazole fibrous materials are a recognized class of fibers exhibiting non-burning characteristics and a great resistance to degradation by heat, hydrolytic, and oxidizing media. Polybenzimidazole fibers are good insulating materials and do not give off toxic fumes when heated. Such fibers particularly are suited for use in applications where high temperature resistance and the safety afforded by a non-combustible fiber is of importance. For instance, such fibers heretofore have been utilized in the production of space suits, parachutes, and ropes intended for use in outer space. Other potential uses for polybenzimidazole fibers include: protective clothing for firemen, operators in steel and glass mills, and pilots of military aircraft; furnishings in critical areas such as carpets, drapes and upholstery, in spacecraft, submarines, commercial aircraft, hospitals, nursing homes, etc.
The polybenzimidazole fibrous materials inherently are of a light gold color to dark brown color. As discussed in commonly assigned U.S. Pat. No. 3,836,500, such fibers commonly darken upon aging.
Polybenzimidazole fibers tend to be relatively amorphous, and are found to possess a greater number of potential acid dye sites than wool. However, prior attempts at the application of any dye class by standard dyeing techniques heretofore has been unsuccessful. When the dyeing of polybenzimidazole fibers has been attempted in the prior art, the dye penetration generally has tended to be poor, and often the dye has been readily removable from the fiber surface. The difficulties encountered when attempting to dye polybenzimidazole fibers may be attributed at least in part to the relatively high glass transition temperature of the same, e.g. 350.degree. to 375.degree.C. There accordingly has remained a need for a reliable technique to satisfactorily dye polybenzimidazole fibers so that aesthetically pleasing shades other than that inherently produced may be combined with its other highly desirable utilitarian characteristics. Also, the ability to provide satisfactorily dyed polybenzimidazole fibrous materials is of importance when the end use is in a fabric intended for forming flight suits where a bright highly visible color is helpful in the spotting of downed aviators in emergency situations.
It is an object of the invention to provide an improved process for the dyeing of polybenzimidazole fibers.
It is an object of the invention to provide an improved process for the dyeing of polybenzimidazole fibers with an anionic dyestuff.
It is an object of the invention to provide an improved process for the dyeing of polybenzimidazole fibers which may be carried out at moderate temperatures substantially below the glass transition temperature of the polybenzimidazole.
It is another object of the invention to provide an improved process for the dyeing of polybenzimidazole fibers wherein complete and uniform dye penetration is accomplished.
It is another object of the invention to provide an improved process for the dyeing of polybenzimidazole fibers wherein the dyed product exhibits satisfactory washfastness, crockfastness, dryclean fastness.
It is a further object of the invention to provide an improved process for the dyeing of polybenzimidazole fibers wherein the dye present in the dyed fibrous product is resistant to sublimation at elevated temperatures.
These and other objects, as well as the scope, nature, and utilization of the process will be apparent from the following description and appended claims.